RESUMO
The giant tortoises of the Galápagos have become greatly depleted since European discovery of the islands in the 16th Century, with populations declining from an estimated 250 000 to between 8000 and 14 000 in the 1970s. Successful tortoise conservation efforts have focused on species recovery, but ecosystem conservation and restoration requires a better understanding of the wider ecological consequences of this drastic reduction in the archipelago's only large native herbivore. We report the first evidence from palaeoecological records of coprophilous fungal spores of the formerly more extensive geographical range of giant tortoises in the highlands of Santa Cruz Island. Upland tortoise populations on Santa Cruz declined 500-700 years ago, likely the result of human impact or possible climatic change. Former freshwater wetlands, a now limited habitat-type, were found to have converted to Sphagnum bogs concomitant with tortoise loss, subsequently leading to the decline of several now-rare or extinct plant species.
Assuntos
Biodiversidade , Tartarugas , Áreas Alagadas , Animais , Carvão Vegetal , Equador , Fezes/microbiologia , Plantas , Esporos Fúngicos/isolamento & purificaçãoRESUMO
Paleoecological evidence from the past 8000 years in the Galápagos Islands shows that six presumed introduced or doubtfully native species (Ageratum conyzoides, Borreria laevis/Diodia radula-type, Brickellia diffusa, Cuphea carthagenensis, Hibiscus diversifolius, and Ranunculus flagelliformis) are in fact native to the archipelago. Fossil pollen and macrofossils from four sites in the highlands of Santa Cruz Island reveal that all were present thousands of years before the advent of human impact, refuting their classification as introduced species. These findings have substantial implications not only for conservation in Galápagos but for the management of introduced species and pantropical weeds in general.
Assuntos
Conservação dos Recursos Naturais , Fósseis , Pólen , Ecologia/métodos , Ecossistema , Equador , Humanos , MagnoliopsidaRESUMO
In tropical rainforests, 30-65% of tree species grow at densities of less than one individual per hectare. At these low population densities, successful cross-pollination relies on synchronous flowering. In rainforests with low climatic seasonality, photoperiodic control is the only reliable mechanism for inducing synchronous flowering. This poses a problem because there is no variation in day length at the Equator. Here we propose a new mechanism of photoperiodic timekeeping based on the perception of variation in sunrise or sunset time, which explains and predicts the annually repeated, staggered, synchronous and bimodal flowering of many tree species in Amazonian rainforests near the Equator.